The primary goal of the proposed research is to examine the transition period following the birth of a baby sibling. The arrival of a newborn sibling often leads to feelings of displacement on the part of the older child and parental concerns about sibling jealousy. Specifically, we propose to examine changes in family relationships (mother-child, father-child, and marital), parent well-being, and the firstborn child's adjustment longitudinally. The study begins in the last trimester of the mother's pregnancy with a second child and continues throughout the first year after the sibling's birth. An important goal of this study is to determine which families may be a greatest risk for a stressful transition. This research proposes to: 1. identify different change trajectories in the firstborn child's adjustment across the first year following the birth of the second child; 2. to examine the interrelations between changes seen in family relationships, parental well-being and the older child's adjustment; 3. to use prenatal assessments of family, child and parent characteristics to predict different developmental trajectories of family and child functioning overtime and; 4. to address the socioemotional development of the young infant throughout the first year following the transition to siblinghood. The proposed research is unique in that it will include a large sample of 200 families; follow these families longitudinally before and after the birth; include both mothers and fathers as participants; and examine this transition from a dynamic ecological systems framework. This developmental study will further our understanding of the transitional stresses experienced by families and guide us in developing preventative recommendations to health care professionals and the families they serve.